There are many important commercial applications of organophosphorus compounds derived from aromatic alcohols which include their use as antioxidants, stabilizers, anti-wear additives, and as ligands for various catalytic processes, for example olefin hydrocyanation or hydroformylation. An ingredient for making some monodentate or bidentate organophosphorus compounds includes 2,2′-biphenol compounds with the general Structure I. These 2,2′-biphenols are generally made by oxidative coupling of the corresponding phenols of Structure II, for example as disclosed in the published U.S. Patent Application 2003/0100802.

One method for manufacturing 2-secondary-alkyl-4,5-di-(normal-alkyl)phenols of general Structure II is the alkylation of corresponding 3,4-di-(normal-alkyl)phenols of general Structure III. Houben-Weyl, Vol. 6/1C pages (955-985), G. Thieme Verlag, Stuttgart 1976, teaches general methods for the alkylation of phenols with alkenes using homogeneous and heterogeneous acid catalysts. With regard to the latter catalysts, U.S. Pat. No. 3,037,052, for example, discloses the use of macroreticular ion exchange resins containing sulfonic acid groups as catalysts for the alkylation of phenols with alkenes. This reference states that “macroreticular” refers to a unique porous structure that is developed when monoethylenically unsaturated monomers are copolymerized with polyvinylidene monomers in the presence of certain compounds.
J. Kamis [Collection of Czechoslovak Chemical Communications 1964, 29(12), 3176-8] reports the alkylation of 3,4-dimethylphenol with the reactive 1,1-disubstituted alkene, isobutylene, in the presence of a cation exchange resin Allassion CS. However, both catalyst activity and selectivity to 2-tertiary-butyl-4,5-dimethylphenol are reported to be low. S. P. Starkov and L. V. Glushkova (Journal of Applied Chemistry of the USSR 1967, 40, pages 209 and 1583) describe the alkylation of 3,4-dimethylphenol with the reactive 1,2-disubstituted alkenes, 2-hexene and cyclohexene, in the presence of the cation exchange resin KU-2. Poor catalyst activity requires high loadings (50%) and 3,4-dimethylphenol conversion is maintained below 50% to achieve acceptable chemical yields to the desired 2-alkyl-4,5-dimethylphenol. High catalyst loadings, low 3,4-dimethylphenol conversion, and low selectivity to the desired 2-alkyl-4,5-di-(normal-alkyl)phenol severely limit reactor productivity and add to the manufacturing cost.
U.S. Pat. No. 4,236,031 discloses a process for preparing 5-t-butyl alkylphenols comprising reacting a 3-alkylphenol or a 2,3-dialkylphenol with isobutylene in the presence of an effective amount of a sulfonated polystyrene catalyst crosslinked with divinylbenzene at a temperature of at least 100° C. U.S. Pat. No. 4,236,031 also discloses a process for preparing 6-t-butyl alkylphenols comprising reacting a 3-alkylphenol or a 2,3-dialkylphenol with isobutylene in the presence of an effective amount of a sulfonated polystyrene catalyst crosslinked with divinylbenzene at a temperature in the range of 50° C. to 90° C. U.S. Pat. No. 4,380,677 discloses the selective dialkylation of 4-alkylphenols with isobutylene using an alkylation catalyst which is a macroreticular cation exchange resin bearing sulfonic acid groups with an internal surface area greater than about 200 square meter per gram (m2/g) and an average pore diameter less than 120 Angstroms (Å).
The use of macroreticular cation exchange resins containing sulfonic acid groups as catalysts for the alkylation of substituted phenols with alkenes has been disclosed. However, the selection and usage of such a catalyst for the selective monoalkylation of 3,4-di-(normal-alkyl)phenols with alkenes to produce 2-secondary-alkyl-4,5-di-(normal-alkyl)phenols and the preferred properties of such a catalyst to reach high productivity in this reaction have not been previously reported. An improved synthesis of 2-secondary-alkyl-4,5-di-(normal-alkyl)phenols is desired. In particular, a process for making the desirable 2-iso-propyl-4,5-dimethylphenol from 3,4-dimethylphenol and propylene that is characterized by the combination of (1) high reaction productivity at low catalyst to reactant ratios, (2) high propylene and 3,4-dimethylphenol conversions, and (3) good selectivity to the 2-iso-propyl-4,5-dimethylphenol isomer is desired. The present invention describes such a process, as well as the associated benefits derived from the separation of 2-iso-propyl-4,5-dimethylphenol from co-products.